The invention relates to an apparatus and method of electrochemical polishing utilizing a ring-form electrode, and in particular to an apparatus and method capable of electrochemical polishing a workpiece continuously processed by a shaping machine.
In the conventional techniques, after a workpiece has been through a shaping process, such as rolling, extrusion and drawing, etc., manual polishing or mechanical burnishing is performed to complete the surface treatment. However, the effectiveness of manual polishing is limited by the experience of the operator, and the man-hours and cost are relatively high. In addition, the contact pressure between the tools used and the workpiece is not so easily controlled during manual polishing or mechanical burnishing, causing the local generation of non-uniform residual stress on the surface of the workpiece. The residual stress is usually higher than the maximum strength of the workpiece; therefore, the surface of the workpiece may collapse and cause the formation of small cavities on the surface of the workpiece. Thus, the life of the workpiece is reduced. In addition, it is difficult to find operators with the technique and experience needed for manual polishing in today""s society. Mechanical burnishing is limited by the shape and characteristics of the machine; as a result, its application is very limited and inconvenient.
Electrochemical processing uses a combination of electric energy and chemical energy. In the electrochemical processing, electrolyte is supplied to the space between the workpiece, connected with the positive pole of the DC power supply, and the tool electrode, connected with the negative pole. The circulation of the electrolyte serves the secondary purpose of removing electrolytic byproducts generated during the electrochemical processing. This method is suitable for materials with high hardness, heat-resistance or corrosion resistance.
Electrochemical polishing is a technique using electrochemical processing to reduce the roughness of the workpiece. It can be applied in research or industry as a highly efficient surface treatment method to obtain a high-quality workpiece without residual stress or burrs.
However, electrochemical polishing is presently limited in application to stainless steel which has been mechanical processed in order to smooth cavities on the surface of the workpiece and prevent the residue from remaining on the surface of the workpiece. The workpiece has better effect about corrosion resisting after electrochemical polishing. However, after such workpiece has been processed by the traditional electrochemical polishing, it must be put in an additional electrolytic tank; hence, the polishing time is much longer and the amount of material removed from the workpiece is extremely little.
Nevertheless, the labor savings and accuracy of electrochemical polishing have lead to continued investigation into its application. Electrochemical techniques such as electrochemical drilling, electrochemical grinding and electrochemical deburring, etc, have been developed. A Japanese company has developed an apparatus for the electrochemical polishing of materials other than stainless steel. However, because the cost of such an apparatus is very expensive and the design of its electrode is very difficult, its practical application is still limited.
In view of the disadvantages of the conventional electrochemical polishing technique, an object of the invention is to provide an electrochemical polishing method and its apparatus using a rotatable ring-form electrode. It offers advantages of economical equipment, a minimum-polluting and low-cost process, and easy assembly and automation. Bars and tubes, produced by traditional machining techniques, for example, turning, drawing, rolling, and extrusion, can be continuously processed by the apparatus of the present invention. A mechanism with a tool electrode, a DC power supply and an electrolysis-supply tank of the present invention can be installed on the traditional production equipment. The tool electrode is connected with the negative pole of the DC power supply, while the workpiece is connected with the positive pole of the DC power supply and kept a fixed distance from the tool electrode. The electrode or the workpiece advances at a predetermined feeding speed while the workpiece is electrochemically polished. The present invention uses the centrifugal force of rotational tool electrode to discharge electrolytic byproducts, making electrochemical polishing more effective. The present invention is also designed to obtain fast improvement of the surface roughness of the workpiece, and to effectively reduce residual stress.
Another purpose of the present invention is to provide an electrode-supporting mechanism with a low-cost tool electrode, easy assembly and rotational power. For the workpiece with circular shape, such as circular tubes or circular rods, the electrode-supporting mechanism of the present invention can be rotated and use the centrifugal force of the rotational tool electrode to discharge the electrolytic byproducts, which makes electrochemical polishing more effective.
Furthermore, another purpose of the present invention is to provide an electrochemical polishing method. The DC power supply, the electrolyte-supplying tank, a pump, a filter and a tube of the present invention can be installed on traditional equipment for drawing, rolling, or extrusion and so on. During electrochemical polishing, the tool electrode is connected with the negative pole of the DC supply power, while the workpiece is connected with the positive pole of the DC supply power. The size of the inner diameter of the ring-from electrode is 0.2xcx9c1.0 mm bigger than the outer diameter of the workpiece. The electrolyte is a solution comprising 20%xcx9c40% of NaCl or NaNO3. The feeding speed of the electrode is about 1.5xcx9c2.5 mm/min, the rating current is about 5xcx9c10 mm/min when the average diameter of the workpiece is 10 mm, the voltage is about 10xcx9c15V, and the width of the pulse is about several to several tenths of a sec.